1. Field of the Invention
This invention relates generally to the field of multimedia systems. More particularly, the invention relates to a system and method for multimedia simulcast using different encryption and/or compression techniques.
2. Description of the Related Art
As illustrated in FIG. 1, the “headend” in a cable television network is the facility where video feeds from various content providers (e.g., HBO, NBC, FOX, . . . etc) are received via satellite dish 108 and/or television antenna 109, processed by headend equipment 100 and transmitted to cable subscribers. Headend equipment 100 for processing the video feeds typically includes one or more MPEG-2 compression modules 101; conditional access (“CA”) encryption modules 103 and 105; and quadrature amplitude modulation (“QAM”) modules 110.
The MPEG-2 compression modules 101 compress any incoming video streams which have not already been compressed according to the MPEG-2 video compression standard. As indicated in FIG. 1, if the video content has already been compressed by the content provider, additional MPEG-2 compression will not be required at the headend (represented by the MPEG-2 stream feeding CA module 105).
Once compressed, the video content may be encrypted by conditional access (“CA”) encryption modules 103, 105 to prevent users from viewing content which they do not have the right to view (e.g., subscription-based content such as HBO or pay-per-view channels). Standard CA encryption systems are well known in the art and are currently manufactured by only a relatively small group of companies including Scientific Atlanta,™ Motorola,™ and News Data Systems.™
As indicated in FIG. 1, not all video content transmitted over cable networks is encrypted. For example, analog channels are transmitted unencrypted over most cable networks. As such, to prevent users from illegally viewing the analog channels, cable companies must physically disconnect the user's home from the cable network (e.g., using remote disconnect mechanisms such as a “trap” or a manual disconnect at the user's home by a cable technician).
The encrypted and/or unencrypted channels are then modulated and statistically multiplexed by a quadrature amplitude modulation (“QAM”) module 110. As is known in the art, QAM uses phase and amplitude shaping to define a string of digital data. Cable companies generally use 64 QAM or 256 QAM modulation techniques, which transmit digital content using 6-bit or 8-bit symbols, respectively. Certain multimedia systems (primarily satellite systems) use a different modulation technique known as Differential Phase Shift Keying (“DPSK”) rather than QAM to modulate the video content. Once the digital content has been QAM-modulated, it is transmitted across the cable system via one or more RF modulators 115. Note that the analog signal in FIG. 1 is fed directly into the RF modulators 115 for transmission over the cable network (i.e., it is not encrypted or QAM-modulated).
As illustrated in FIG. 1, an allocation of all available bandwidth 120 on a cable network typically includes an unencrypted analog component 121, a compressed and encrypted digital component 122 (compressed via MPEG-2 and encrypted using standard encryption as described above), and a third miscellaneous component 123 reserved for transmitting various types of control signals and data (e.g., according to the DOCSIS cable modem standard).
As illustrated in FIG. 2, a typical multimedia receiver 120 (referred to generally as a “set-top box”) for receiving cable or satellite channels includes one or more tuners 210 which lock on to the video signal 200 at a particular carrier frequency and down-convert the signal to a baseband signal. A QAM demodulator 220 then demodulates the baseband video signals; a CA decryption module 230 decrypts the digital video content contained in the video signal 270 using a series of decryption keys provided via a secure micro unit (not shown); and an MPEG-2 decoder module 240 decompresses the content. An NTSC encoder 250 may also be used to encode the digital video content so that it may be properly displayed on a standard NTSC television 260. As indicated in FIG. 2, if the analog signal 271 is not encrypted, it may be transmitted directly through to the television 260 following demodulation.
One problem which exists with the foregoing configuration is that cable operators are unable to change the types of encryption and/or compression used for transmitting video content without upgrading all of the multimedia receivers used by current subscribers. For example, the standard CA decryption modules 230 found in current multimedia receivers are incapable of decrypting content using a non-standard encryption algorithm. Similarly, multimedia receivers equipped with MPEG-2 decoder modules 240 are only capable of decompressing video content according to the MPEG-2 standard. As such, cable operators are unable to realize the benefits of more advanced compression algorithms (e.g., such as MPEG-4 and RealVideo™ 8), and/or alternative, open encryption techniques.
Accordingly, what is needed is a system and method which will allow cable operators to implement different compression and/or encryption techniques without upgrading multimedia receivers used by current subscribers. What is also needed is a system and method which will allow cable operators to seamlessly integrate more advanced compression and encryption techniques as those techniques are developed.